Forced flow vaporizer for compression type refrigerating equipment

ABSTRACT

The invention relates to a forced flow vaporizer for compression type refrigeration equipment which vaporizer includes a pipe through which refrigerant flows. The effective outside radiating surface of the pipe is increased with fins and mesh inserts are disposed interiorly of the pipe, the fins and inserts only being provided for the straight portions of the pipe.

O Umted States Patent 1 1 [111 3,740,967 Huelle June 26, 1973 FORCED-FLOW VAPORIZER FOR [56] References Cited EQUIPMENT 2,702,460 2/1955 Gaugler 62/527 [75] Inventor: Zbigniew Ryszard Huelle, 3,197,975 8/1965 Boling 62/515 Sonderberg, Denmark [73] Assignee: Danfoss A/S, Nordberg, Denmark Primary Examiner-Meyer Peru Attorney-Wayne B. Easton [22] Filed: Apr. 7, 1971 [21] Appl. N03 131,913 57 ABSTRACT The invention relates to a forced flow vaporizer for [30] Foreign Application Prlorlty Data compression type refrigeration equipment which va- Mar. 23, 1970 Germany P 20 12 808.3 porizer includes a pipe through which refrigerant flows.

The effective outside radiating surface of the pipe is in- [52] 11.8. CI. 62/527, 165/179 creased with fins and mesh inserts are disposed i t i [5 l Int. Cl. F25b 41/04 orly of the pipe, the fins and inserts only being provided [58] Field of Search 165/179; 62/515, for the straight portions of the pipe.

l 1 Claim, 2 Drawing Figures EJfllllll llll/ll l|ll ll |llI-lll 9 )jlllylylllll FORCED-FLOW VAPORIZER FOR COMPRESSION-TYPE REFRIGERATING EQUIPMENT This invention relates to a forced-flow vaporizer for compression-type refrigerating equipment and having a pipe through which refrigerant flows and at the end of which only refrigerant vapour emerges.

The capacity of a refrigerator operating on the forced-flow principle depends to a large extent upon the pressure-drop that the refrigerant undergoes when passing through the vaporizer. In the majority of cases use is made of forced-flow vaporizers comprising a single long pipe or an equivalent duct, at the end of which is located a sensor which effects interruption of the supply of refrigerant when the latter is not fully vaporized upon emerging from the pipe. For reasons of safety, only that section of the pipe directly in front of the sensor should be used for bringing the refrigerant into a superheated state, so that the total state of fill of the vaporizer is not quite 100 percent. A certain length of pipe is necessary for effecting complete vaporization of the refrigerant. If a pipe having a smooth interior and exterior is used, and when fairly high refrigerating ca pacity is required, the requisite lengths of pipe become so great that the pressure-drop occurring in the vaporizer pipe calls for excessively high operating power for the refrigerating machine.

For this reason, it is known, for the purpose of conveying fairly high quantities of refrigerant to use a plurality of vaporizer pipes arranged in parallel, with the result that the pressure-drop can be very considerably reduced. This expedient however necessitates the use of a distributing arrangement at the inlet to the bank of pipes, which arrangement uniformly distributes the refrigerant to the various pipes. Also a refrigerant sensor in a superheating zone provided at its input side is required at the end of each pipe. This leads to a considerably more costly construction and to a marked reduction, e.g., by 30 percent or more, in the total'state of fill of the pipe system.

It is also usual to increase the effective outside radiating surface of a vaporizer pipe by means of fins or the like. This arrangement is intended to increase the refrigerating capacity provided for each unit of length of the pipe to an extent corresponding to the increase in surface. The application of this principle to the inside of the pipe fails, however, because the inwardly projecting fins or the like increase the resistance to flow in the vaporizer pipe to such an extent that, other conditions being equal, a refrigerating machine of higher power has to be used than would otherwise be necessary.

It is further known to use a flooded vaporizer in which a mesh insert, which only slightly reduces the inside cross-section of the bore, is located closely against the inside surface. The purpose of this insert is to trap liquid which may be present on the inside wall of the pipe, so that it is not entrained in the refrigerant vapour. It is further known to employ the same means in the case of a vaporizer for an absorption-type refrigerating system. The arrangement is in this case intended to cause wetting of the inner wall of the pipe over a greater area than that corresponding to the normal state of fill of the system.

The object of the invention is to provide a forcedflow vaporizer for compression-type refrigerating equipment in which, for a given transmitted refrigerating capacity, both an extremely small pressure-drop and a very high state of fill of the system are achieved.

According to the invention, there is provided a forced-flow vaporizer for compression-type refrigerating equipment having a pipe through which in operation a refrigerant flows and at the end of which only refrigerant vapour emerges, and in which the effective outside radiating vapour emerges, and in which the effective outside reaiating surface of the pipe is increased by the provision of fins or the equivalent, the inner surface of the pipe is smooth and the pipe accommodates a mesh insert, which only slightly reduces the effective internal cross-section of the pipe the mesh insert being disposed closely against the inner surface of the pipe.

The mesh insert only slightly increases the resistance to flow of the vaporizer pipe. On the other hand however, the combination of features specified makes it possible to obtain coefficients of heat transmission k, hitherto not attainable, for the transfer of heat between the refrigerant and the medium to be cooled, in particular air. Whereas the highest values for k hitherto attainable were in the order of 12 13, a coefficient of heat transmission of more than 20 can be obtained by means of the invention. Consequently, the length of the pipe can be considerably shortened for a prescribed transferred refrigerating capacity, and the pressuredrop can be reduced to a considerably lower value. If this principle is applied to two or more pipes arranged in parallel, very much greater refrigerating capacities than heretofore can be transferred under otherwise similar conditions.

The straight portions of the pipes of a vaporizer are frequently interconnected by means of return bends and in applying a feature of the invention the fins and the mesh inserts are provided only along the straight portions of the pipes. Since the return bends constitute only a small part of the entire vaporizer pipe, it suffices to apply the measures for increasing the coefficient of heat transmission only to the straight portions. In this way, the fine, e.g., common fins, for all the straight pipe portions as well as the mesh inserts which can be inserted into the pipe-portion at one of its end-faces, can be more readily fitted.

In applying a further advantageous feature of the invention each mesh insert consists of an elongate, flat length of mesh material, the width of which is some what smaller than the inside circumference of the pipe and which, prior to insertion in the pipe is bent to form a tube of generally circular cross-section biassed to a diameter less than that of the pipe, the material of the mesh being such that on insertion into the pipe the mesh tube will expand and closely engage the inner surface of the pipe. This results not only in greater ease of manufacture of the inserts from flat mesh material, but also facilitates the introduction of the insert into the pipe and enables the bias to be selected with precision.

In applying a further feature of the invention, the edges of the elements of mesh material are so arranged that they form a gap at the bottom of the interior of the pipe. If oil is separated out in the vaporizer, it can flow away through the gap. The required position of the channel provided by the gap can be best achieved if each straight portion of the pipe is provided with a separate mesh insert.

In the constructional arrangement described, heat transfer is achieved on the outside by an increase in area, and on the inside by increased degree of wetting.

Only by combining the two improvements, is it possible to effect a marked improvement in heat transmission such as could never be achieved by a measure affecting only the outside or only the inside of the pipe.

The invention will now be described in more detail by reference to an embodiment illustrated in the drawing, in which:

FIG. 1 is a schematic longitudinal section through a vaporizer for use in compression-type equipment; and

FIG. 2 is a diagrammatic cross-section of the vaporizer shown to a larger scale than FIG. 1.

Referring to FIG. 1, a refrigerant compressor 1 passes refrigerant into a vaporizer 2 by way of a pressure pipe. The vaporizer 2 feeds liquid refrigerant into a vaporizer 4, the flow of refrigerant being controlled by an expansion valve 3. The vaporized refrigerant returns to the compressor 1 through a vacuum pipe. The expansion valve 3 is controlled by a temperature sensor 5, which is fitted at the outlet 6 of the vaporizer 4.

The vaporizer 4 has a single pipe 7 consisting of stright portions 8 and return bends 9 interconnecting the straight portions. The pipe is held in supports 10 at each end. The straight portions 8 of the pipe have common heat-transfer fins 11. A mesh insert 12 is pushed into each straight portion of pipe. The air to be cooled flows in a direction parallel with the fins 11.

The inserts 12 are shown only diagrammatically. Advantageously, they are made of metal gauze produced in flat pieces. Strip elements cut from these pieces, are bent to the shape of a tube and are inserted into the straight portions 8 of pipe in a biassed condition before these straight portions have been interconnected by means of the return bends 9. By biassed condition is meant that the strip gauze elements when bent into tubular form, tend by their nature to expand to a larger diameter. Thus, when they have been inserted in the pipe sections they will expand so as closely to engage the inner pipe walls to leave gaps 13 between their opposing edges. The elements are positioned so that the gaps 13 are positioned at the bottoms of the pipe sections 8.

In a construction in accordance with the invention, a heat-transfer coefficient a, of 25 was recorded on the outside and a heat-transfer coefficient 01 of 1,400 on the inside, and the ratio of the outside area to the inside area was found to be 13.7. This resulted in a coefficient of heat transmission k of 20, this value not having previously been attained in the case of forced-flow vaporiz ers for the cooling of air.

What I claim is:

1. A forced-flow vaporizer for compression-type refrigerating equipment comprising a pipe for conveying a refrigerant therethrough, fins for increasing the outside radiating surface of the pipe, said pipe having a smooth inner surface, mesh inserts disposed in said pipe in close engagement with said inner surface, said pipe having straight portions interconnected by return bends, said tins and mesh inserts being provided only along the straight portions of said pipe, each of said mesh inserts consisting of an element of mesh material having a circumference which is slightly larger than the internal circumference of said pipe and which has a resilience causing it to be resiliently biased and expanded against said inner surface of said pipe, at least one of said inserts having opposing longitudinally extending edges located at the bottom of the interior of one of said pipe portions to form a longitudinally extending gap. 

1. A forced-flow vaporizer for compression-type refrigerating equipment comprising a pipe for conveying a refrigerant therethrough, fins for increasing the outside radiating surface of the pipe, said pipe having a smooth inner surface, mesh inserts disposed in said pipe in close engagement with said inner surface, said pipe having straight portions interconnected by return bends, said fins and mesh inserts being provided only along the straight portions of said pipe, each of said mesh inserts consisting of an element of mesh material having a circumference which is slightly larger than the internal circumference of said pipe and which has a resilience causing it to be resiliently biased and expanded against said inner surface of said pipe, at least one of said inserts having opposing longitudinally extending edges located at the bottom of the interior of one of said pipe portions to form a longitudinally extending gap. 